Re: Re: Missing rows with index scan when collation is not "C" (PostgreSQL 9.5)

Peter Geoghegan <pg@heroku.com> writes:
> On Wed, Mar 23, 2016 at 11:04 AM, Magnus Hagander <magnus@hagander.net> wrote:
>> That said, my main point is that I do not think the knob is something that
>> should be tuned by the average end user. For most people, that should be
>> left to the packagers for the platform, who can make an informed choice
>> about if it's safe to turn it on.

> I could get behind that if we really make an effort to help them make
> an informed choice. The abbreviated keys optimization is highly
> valuable, and I put a lot of work into it, as did Robert.

I realize that, and I'm sympathetic, but I'm afraid it also means that
your judgment in this matter is rather biased.

I do not think that end users can be expected to know whether this is safe
to turn on, and TBH I do not think that most packagers will either.  My
opinion is that our only guaranteed-safe option is to turn it off, period,
no exceptions for platforms that we've not yet found a failure case for.
We can consider turning it back on later, once we've done vastly more
study and testing than has evidently been done to date.  One thing I'm
going to want to know is what was the root cause of glibc's bug, and what
is the reason to think that other implementations are going to be any more
reliable.  At this point I'm disinclined to trust any implementation that
can't point to a structural reason (e.g., sharing code) to believe that
strcoll and strxfrm must yield equivalent answers.

(In other words, I want an #ifdef NOT_USED, which is even less effort
than either a GUC or a configure option ;-(.  As well as being something
that we won't need to document and support indefinitely.)

            regards, tom lane